Don't do it! it took me a year or more to realise that its more sensible (Cheaper and more feature-packed) to use an external sequencer so I bought a second hand Beatstep Pro.
Its an easy way to add structure and repetition to my mostly generative rack and is so much easier than programming drums on my Robaux LL8, though they are cracking little drum sequencers.
Enjoy your spare HP, don't rush to fill every last space, this is not like filling sticker books. Resist the urge to 'complete' your rack, its never complete so just relax.